Field of the Invention
The present invention is broadly concerned with improved extruders and screw configurations designed for the economical production of animal feed products containing high quantities of fibrous ingredients. More particularly, it is concerned with such extrusion equipment which is capable of processing feed products, e.g., aquatic feeds, containing in excess of 20% by weight of fibrous ingredients at commercially acceptable production rates.
Description of the Prior Art
The aquaculture industry commonly makes use of extruded feed products having various nutritional profiles and operational characteristics, such as sink rates. For example, an acceptable salmon feed would have very different properties as compared with a shrimp feed. Accordingly, in the production of these feeds, the ingredients must be carefully selected and processed so as to achieve the optimal feed for a particular aquatic creature.
Many aquatic feeds rely on expensive ingredients, such as fish meal, to provide appropriate levels of nutrition and operational characteristics. In an effort to reduce costs, processors have endeavored to use less expensive, fibrous ingredients (e.g., rice byproducts) as at least a partial substitute for higher value ingredients. However, these fibrous ingredients when used at levels above about 20% by weight, can be difficult to extrude at commercially useful rates. That is, while conventional extrusion equipment can process high fibrous ingredient feeds, the normal throughput for such equipment is significantly reduced, perhaps as much as 50%. If this equipment is operated at normal production rates, the resultant feeds are structurally weak and tend to crumble, and are not acceptable to end users. Accordingly, it has heretofore not been practical to use high levels of fibrous ingredients in aqua feeds, notwithstanding the potential cost savings which could be realized with such feed formulas.
There is accordingly a need in the art for improved extrusion equipment and processes which can provide fully acceptable aqua feeds having levels of fibrous ingredients above 20% by weight, while still achieving production throughputs making the feeds economically advantageous.